Automatic equalization system in FM communication circuit

Abstract

An automatic amplitude and phase equalization system in an FM communication circuit, in which a pilot signal included in a baseband signal of a transmitted FM signal demodulated by an FM demodulator is extracted and frequency-multiplied, a high harmonic wave of the pilot signal generated in the baseband signal is phase-detected using the frequency-multiplied output as a reference signal, an amplitude equalizer provided before the FM demodulator is driven by a component included in the phase detected output and of the same phase as the reference signal, and a phase equalizer provided before the FM demodulator is driven by a component included in the phase detected output and orthogonal to the reference signal, whereby amplitude and phase characteristics of a transmission path of the FM signal are automatically equalized.

What we claim is: 
     
       1. An automatic phase equalization system in an FM communication circuit comprising: input terminal means for receiving a transmitted FM signal;   variable phase equalizer means connected to said input terminal means to develop an equalized output from said transmitted FM signal;   FM demodulator means connected to said variable phase equalizer means to provide an demodulated baseband output from said equalized output;   first filter means connected to said FM demodulator means for obtaining at least one harmonic wave of a pilot signal included in said demodulated baseband output;   second filter means connected to said FM demodulator means for obtaining said pilot signal;   frequency multiplying means connected to said second filter means to obtain at least one reference wave by frequency-multiplying said pilot signal from said second filter means;   phase detector means connected to said first filter means and said frequency multiplying means to phase-detect said harmonic wave by the use of said reference wave as a reference so as to develop at least one detected output;   control means connected to said phase detector means and said variable phase equalizer means for controlling said variable phase equalizer means by the detected output to reduce the level of said harmonic wave; and   output terminal means connected to said FM demodulator means for obtaining the demodulated baseband signal.   
     
     
       2. An automatic phase and amplitude equalization system in an FM communication circuit comprising: input terminal means for receiving a transmitted FM signal;   equalizer means connected to said input terminal means and comprising a cascade connection of variable phase equalizer means and variable amplitude equalizer means to develop an equalized output from said transmitted FM signal;   FM demodulator means connected to said equalizer means to provide an demodulated baseband output from said equalized output;   first filter means connected to said FM demodulator means for obtaining at least one harmonic wave of a pilot signal included in said demodulated baseband output;   second filter means connected to said FM demodulator means for obtaining said pilot signal;   frequency multiplying means connected to said second filter means to obtaining at least one first reference wave and at lease one second reference wave by frequency-multiplying said pilot signal from said second filter, said second reference wave having a phase difference of 90° with respect to said first reference wave;   first phase detector means connected to said first filter means and said frequency multiplying means to phase-detect said harmonic wave by the use of said first reference wave as a reference so as to develop at least one first detected output;   second phase detector means connected to said first filter means and said frequency multiplying means to phase-detect said harmonic wave by the use of said second reference wave as a reference so as to develop at least one second detected output;   first control means connected to said equalizer means and said first phase detector means for controlling said variable phase equalizer means by the first detected output to reduce the level of said harmonic wave;   second control means connected to said equalizer means and said second phase detector means for controlling said variable amplitude equalizer means by the second detected output to reduce the level of said harmonic wave; and   output terminal means connected to said FM demodulator means for obtaining the demodulated baseband signal.